In communications networks, for data forwarding device such as switch or router, it is advantageous for data security and utilization of network resources to forward network data by subscriber groups. For instance, suppose there is a multicasting group G in a communication network, a query message is sent a certain time period after the router forwards the data for said multicasting group G to verify whether any member of said multicasting group G still exists, and members in said multicasting group G sends Internet Group Management Protocol (IGMP) messages again to respond to said query message; in case that no member of said multicasting group exists in the network, the router receives no response, then the router tries to query again, and if the router still receives no message, it deems no member of said multicasting group G exists in the network and then stop forwarding data for said multicasting group G. Due to the fact that data forwarding with said multicasting group management method is more specific when compared to broadcasting mode, data security and forwarding efficiency are higher.
However, traditional LANs using IEEE 802.1x protocol can only implement port-based multicasting control, i.e., add subscribers to multicasting groups through adding ports to those multicasting groups. When a request for joining in a multicasting group is sent from a subscriber's terminal, the network switching device, according to the circumstance, adds the MAC address of said terminal to said multicasting group so as to add the subscriber to said multicasting group. Such a method only provides port number and MAC address of the subscriber's terminal rather than subscriber information, therefore any control related with said subscriber can't be performed due to lack of subscriber information. Though IEEE 802.1X protocol is a port-based network access control protocol, which supports subscriber management and accepts multi-subscriber authentication through a single port, such capability can't be utilized to control addition of subscribers to a multicasting group, resulting in uncontrollability of addition of subscribers to a multicasting group.